xjasonlyu/tun2socks

package dialer

import (
    "encoding/binary"
    "net"
    "syscall"
    "unsafe"

    "golang.org/x/sys/windows"
)

const (
    IP_UNICAST_IF   = 31
    IPV6_UNICAST_IF = 31
)

func setSocketOptions(network, address string, c syscall.RawConn, opts *Options) (err error) {
    if opts == nil || !isTCPSocket(network) && !isUDPSocket(network) {
        return
    }

    var innerErr error
    err = c.Control(func(fd uintptr) {
        host, _, _ := net.SplitHostPort(address)
        ip := net.ParseIP(host)
        if ip != nil && !ip.IsGlobalUnicast() {
            return
        }

        if opts.InterfaceIndex == 0 && opts.InterfaceName != "" {
            if iface, err := net.InterfaceByName(opts.InterfaceName); err == nil {
                opts.InterfaceIndex = iface.Index
            }
        }

        if opts.InterfaceIndex != 0 {
            switch network {
            case "tcp4", "udp4":
                innerErr = bindSocketToInterface4(windows.Handle(fd), uint32(opts.InterfaceIndex))
            case "tcp6", "udp6":
                innerErr = bindSocketToInterface6(windows.Handle(fd), uint32(opts.InterfaceIndex))
                if network == "udp6" && ip == nil {
                    // The underlying IP net maybe IPv4 even if the `network` param is `udp6`,
                    // so we should bind socket to interface4 at the same time.
                    innerErr = bindSocketToInterface4(windows.Handle(fd), uint32(opts.InterfaceIndex))
                }
            }
        }
    })

    if innerErr != nil {
        err = innerErr
    }
    return
}

func bindSocketToInterface4(handle windows.Handle, index uint32) error {
    // For IPv4, this parameter must be an interface index in network byte order.
    // Ref: https://learn.microsoft.com/en-us/windows/win32/winsock/ipproto-ip-socket-options
    var bytes [4]byte
    binary.BigEndian.PutUint32(bytes[:], index)
    index = *(*uint32)(unsafe.Pointer(&bytes[0]))
    return windows.SetsockoptInt(handle, windows.IPPROTO_IP, IP_UNICAST_IF, int(index))
}

func bindSocketToInterface6(handle windows.Handle, index uint32) error {
    return windows.SetsockoptInt(handle, windows.IPPROTO_IPV6, IPV6_UNICAST_IF, int(index))
}